plug in manager issue

Hello everybody
Once a new collection created, it is impossible for me to add a new plug in to it.
Cubase boots, detects the new plug in then I got the message “Cubase stop working”, so i restart Cubase but the new plug in doesn’t show up in my new collection, eventhough I scan for new plug in. But when i go back to default collection, the new plug in is listed but it’s impossible to modify my new collection. is it a bug???
Anyhelp welcome, thx